Tapentadol undergoes extensive metabolism, including first pass metabolism. Tapentadol is metabolized primarily via phase 2 glucuronidation to Tapentadol-O-glucuronide and metabolized to a lesser degree by CYP2C9 andCYP2C19 to Desmethyl-Tapentadol (13%), and CYP2D6 to Hydroxytapentadol (2%) (Terlindenet al., 2010;Terlindenet al., 2007). In-vitro studies did not reveal a potential of Tapentadol to either inhibit or induce cytochrome P450 enzymes. Tapentadol is excreted in the urine (99%: 70% conjugated metabolites; 3% unchanged substance)
I used to rotate on and off Tapentadol and AFAIK there are 9 metabolites in total, with three main metabolites. Though all the metabolites of Tapentadol are pharmacologically inactive and the parent molecule appears to be the only active molecule. This profile reduces the probability of large individual variations in the pharmacological effects of Tapentadol. (Tzschentkeet al., 2007).
Though the three main metabolites are:
i) Tapentadol-O-Glucuronide
ii) Desmethyl-Tapentadol
iii) Hydroxytapentadol